The
"Bowtie" is part of the "ThrU-Turn" family of innovative concepts. In
this sketch of a major arterial, traffic making a U-turn around the
ellipse can merge with oncoming traffic, eliminating the need to install
a signal that would stop oncoming traffic as necessary with a Loon. The
median can be landscaped, or potentially used as a major transit
station.

Traditionally, It's Either Form OR Function

All over the nation, planners and residents
alike hope to reinvent languishing suburban retail corridors into
sustainable, livable, transit and pedestrian-oriented "Places" within
the midst of their stale, Anywhere USA sprawl. But the exciting
Visions created by well-meaning stakeholders, planners, and architects
often bump up against a hard reality: The streets in question often
carry huge traffic loads and it is extremely difficult to acquire the
space for desired "Complete Streets."

Another sad truth is that even the best Transit Oriented Development
will still generate a lot of vehicle traffic. If the roadways that serve
proposed TOD are too congested, builders and city councils may be too
reluctant to create TOD because it adds traffic to already intolerable
congestion!

And engineers charged with managing the street simply will not accept
form over function. In truth, to be truly livable and to sustain
desired TOD densities, these intersections need to flow well.
"ThrU-Turns" describe a family of designs such as Median U-turns,
Bowties, Loons. These are hot new designs with excellent Place-Making
qualities as well as exceptional ability to move a lot of traffic at
slower maximum speeds, but higher average speeds, without congestion
through sensitive mixed-use, multi-modal areas.

Place-Making Form AND Engineering Function!

Have you ever tried to turn left from a
parking lot onto a busy arterial, and found it so impossible to get a
gap in both directions that you instead went right, then made a
U-turn? Thru-Turn designs such as Median U-turns, Bowties, Loons,
Superstreet Intersections, Michigan Lefts, and even Roundabouts
successfully formalize this action with amazing results.

ThrU-Turn accomplished using a Bowtie concept. Retail-oriented roundabouts on a low-speed, pedestrian-oriented cross-street.

How do they work?

In the diagrams, some lefts are completed
as "right-U-through." Others are "through-U-right." Either
way, the result is that the former left turn pocket is no longer needed,
so fill it with a transitway, or whatever Place-Making architects can
dream up! And since there are no left-turn arrows, the
intersection can handle more traffic with significantly less delay, and
it is also much easier for pedestrians to cross.

Meet the family

Decades ago, transportation engineers
recognized that if you forced traffic to go "through-U-right", it would
eliminate the need for left-turn arrows, resulting in far less
congestion. Michigan took it to heart. It takes a lot of space for large
vehicles to make a U-turn, and Michigan engineers required that
hundreds of miles of roadway include extra-wide medians to accommodate
these U-turns.

But what can you do if past planners and engineers didn't bless you
with wide medians? A "Loon" is a great variation that simply carves out a
small piece of a convenient parking lot to create enough space for
trucks to make the turn. The required carve-out resembles the head of a
loon, as shown here.

The "Loon" design for carving out enough space for a Thru-Turn

Bowties are another creative innovation that add wonders to the form
and can also improve the function beyond that of a normal Median-U. The
Bowtie uses two roundabouts or ellipses, the centers of which can be
used for stately shade trees, pedestrian refuge, or even transit
stations. Where Loons and Median U's require a signal to stop oncoming
traffic while vehicles U-turn, roundabouts and ellipses do not
necessarily need to stop oncoming traffic with a mid-block signal.

Politically Flexible

The mayor loves the monument he can fit
into the Bowtie's ellipses, but just can't get support from the DOT nor
residents for "Through-U-Rights." No problem! Just build the ellipses or
roundabouts anyway, but still allow people to turn left at the main
intersection as usual. The ellipses serve a useful traffic calming
function. They define an "entry zone" into a more pedestrian-oriented
place, and you have also gained a "Get out of jail free" card where if
traffic ever gets bad enough, just put up signs showing the new way to
go left, and voila!

Disadvantages

Out of direction travel

Initial confusion for drivers

Space required for bulb-outs

Costs a little more than traditional

Utah's First Thru-Turn, Summer of 2011

Median U-Turns are commond in Michigan, and
exist in several other states. Bowties and Loons operate similarly but
are rare by comparison. Utah will soon build its first ThrU-Turn
at 123rd South and Minuteman Drive near I-15 in Draper. The images below
are from a nice video presentation at: http://www.udot.utah.gov/thruturn/

In
Septemeber 2009, Metro Analytics developed the initial concept for this
ThrU-Turn intersection in Draper, Utah. The City was excited about the
posibilities, and together with UDOT sponsored a study to evaluate
several options and ultimately determined to build a variation of that
initial concept. For that study, Avenue Consultants conducted traffic
engineering and simulation, and Metro Analytics provided future volume
estimates. The project is scheduled to begin construction in 2011.

Sign showing drivers the new way to make a left.

Vehicles
on the "Thru-U-Right" path, instead of using a left-turn arrow, which
causes significant delay. See this video and learn more at:
http://www.udot.utah.gov/thruturn/

The 123rd South ThrU-Turn in Draper, Utah, is expected to reduce average 2030 delay from 2-minutes to just 26-seconds!

ThrU-Turns are "Alternative Intersections"

The Thru-Turn family, along with several
cousins such as Town Center Intersections, Continuous Flow
Intersections, Quadrant Intersections, and others are among a series of
concepts collectively known as Alternative Intersections, Alternative
Intersections, or even Unconventional Intersections. The key trait that
links all Alternative Intersections is that they successfully eliminate
the "left-turn arrow" phase, which otherwise reduces intersection
efficiency considerably.

Where can I learn more?

Thru-Turns and other Alternative Intersections can all be found at
www.alternativeintersections.org,
where you can search for every Alternative Intersection that exists or
has been planned anywhere in the world. If you see we are missing some,
register and add them!